1. Field of the Invention
This invention concerns a thermal head for use in a thermal printer and, more specifically, it relates to an improvement for the protruding structure in a heat generating portion.
2. Description of the Prior Art
A thermal head mounted to a thermal printer comprises, for example, a plurality of heat generating resistance elements arranged linearly on an identical substrate, which are heated by electric supply for developing color and performing recording on a heat sensitive recording paper or transferring and performing recording on a common paper by way of an ink ribbon in accordance with this invention.
A thermal head has been prepared so far, for example, as shown in FIG. 4 by partially forming a glass glaze layer 2 on an insulating substrate 1 made of alumina or the like and, further laminating thereover, a heat generating resistance layer 3 made of Ta.sub.2 N or the like, an electric power supplying conductor layer 4 made of Al, Ni or the like, an oxidation preventive layer 5 made of SiO.sub.2 or the like and a wear resistance layer 6 made of Ta.sub.2 O.sub.5 or the like successively. In this case, the electric power supplying conductor layer 4 is patterned into a plurality of individual electrodes and a common electrode, between which heat generating portions A are formed. The heat generating portion A is formed at a portion protruded by the glass glaze layer 2, by which a favorable contact with the recording paper or ink ribbon is attained.
Recently, it has been required to the thermal head that recording is possible with a flat surface paper and that a high speed recording is possible. In order to realize the requirements, it is necessary to increase the heat efficiency by improving the heat conductivity of the heat generating portion.
When forming the glass glaze layer 2 on the insulating substrate 1 in the conventional thermal head, a paste prepared by mixing a glass frit and a binder is coated by printing on the insulating substrate 1 followed by sintering. However, the paste as described above, when coated on the insulating substrate 1, spreads laterally due to the surface tension failing to effectively protrude the heat generating portion A. Specifically, the glass glaze layer 2 has a height h of about 40 .mu.m and the lateral width w of about 500-700 .mu.m, which is actually extremely flat. Then, the effect of improving the contact of the heat generating portion A is poor failing to improve the heat efficiency sufficiently.